21 September 2020

48 KBaud OQPSK unid wideband transmissions


This post originates from an email from my friend KE9NS Darrin who noticed  a strange transmission around 6.8 MHz with an occupied bandwidth of about 48 KHz. According to his reports, the signal seems to start somewhere between 0000 and 0100 UTC, likely ON until sun rise. Interestingly, the signal tends to move around the band slightly probably trying to find an open slot in the band. Indeed, some breaks were observed and Darrin just noted that when it shut down for a break there was a STANAG 4285 signal within its 48 KHz passband: it must have realized and moved to an open spot.
Darrin kindly sent me his IQ recordings for analysys since it's impossible for me to get such samples using remote KiwiSDRs.

The waveform has a speed of 48000 Baud and occupies a band of about 48 KHz: as shown in Figure 1, the spectrum width, equal to the manipulation speed and the presence of the third line in the 4th power, lead to think to the Offset QPSK (OQPSK) modulation.

Fig. 1
Although GMSK and OQPSK have a lot in common, some further clues in favor of OQPSK come from the phase plane (Figs. 2a, 2b): OQPSK looks like GMSK with BT < 0.25 (the lower the BT index, the more it's similar to OQPSK).

Fig. 2a - OQPSK phase plane

Fig. 2b - syntesized OQPSK signal
 
Similar results were obtained from the analysis of CIS-1280 waveform (Figure 3).
 
Fig. 3 - CIS-1280 OQPSK waveform

OQPSK is a constant-envelope modulation that has no 180-deg phase shifts and, therefore, has a much higher spectral containment than non-offset QPSK when transmitted over band-limited nonlinear channels. To further bandlimit an OQPSK signal, Shaped OQPSK (SOQPSK) was introduced and its initial version was referred to as MIL-STD SOQPSK after it was adopted as part of a military standard. 
 
Since OQPSK is like a GMSK with a small index, it is possible to do some demodulation attempts using the "FSK3 method" introduced by guys from radioscanner.ru [1]. In this regard, I also tried that FSK3 method by demodulating the 48 KBaud signal on three FSK levels (Figure 4) and then appropriately converting the ternary symbols through a small program written with Octave. It is difficult to establish the accuracy of the final bitstream, anyway the links to download the intermediate FSK3 file are below: everyone can try the demodulation by following the method described and post their comments and the obtained bitstreams.

Fig. 4 - FSK3 demodulation

Back to the 48 KBaud signal, it's always very strong, likely a very powerful transmitter. Quoting Darrin "Its a long shot but, the company that was supposedly trying to transmit stock trades via HF radio has a radio tower located in a town near to me. Supposedly they have a huge antenna array in Elburn, IL and transmit 20kw with an ERP of 808kw (very big stacked curtain log-periodic antennas) pointed 48deg and a special FCC license. It turns out, that antenna array is pointed directly towards my home in Bartlett, IL". We also thought of 188-110D App.D (per STANAG-5069) tests but such a waveform is not indicated.

https://yadi.sk/d/J76M1y-l-u42Sg (wav file) 
https://yadi.sk/d/_3o-UTVKEQpKNw (FSK3 demod)

[1] http://www.radioscanner.ru/forum/topic43183.html#msg865791

11 September 2020

110-220Bd/330 FSK, TMS-430/TC-535 (Swiss Army)

I56578, cryptomaster



This is the well-known Swiss Army 220Bd/330 FSK system consisting of the Telematik-Set 430 (TMS-430) [1] in combination with the cipher device TC-535 [2], the utilized HF transceiver is most likely the SE-430 [3]. This signal is commonly logged as "TMS-430", although TMS-430 is actually the DTE device, while the modem function is performed by TC-535 in conjunction wih SE-430.
These transmissions can be heard almost every day on 4495 KHz (CF) around 1800 UTC, a list of frequencies (apparently constant) at which this signal was noted is: 3502 4594 5182 and 5202 kHz; old logs also reports the 120Bd waveform. Recordings used in this analysis were made thanks to the Twente WebSDR and refer to the 4495 KHz channel. 
 
Looking carefully at the signal, it's possible to note short initial segments which are sent at the speed of 110Bd (Figure 1):
 
Fig. 1 - initial segment sent at 110Bd
 
This apparently oddity intrigued me and my friend cryptomaster and so we decided to study the demodulated streams in more detail. Since the TC-535 is directly connected to the HF transceiver, from the analysis of the stream it is possible to trace and verify the operating phases of the cipher. It's to be mentioned that, given the two speeds, the streams were obtained by demodulating the signal from time to time at 110 or 220 Baud depending on the bit segment that had to be studied; the demodulation speed used for a given figure is shown in its caption.
TC-535 Synchronization sequence (COMSEC preamble) consists of a PN (Pseudo Noise) sequence termed as "Synchronizing Template" sent at the speed of 220 Baud (Figure 2). In addition to synchronization, the PN sequence is also used for (encrypted) commands transmission.  Grouping the PN sequences into a single stream and analyzing it, turns out the presence of the polynomial x^7+x^3+1: likely this is just the 7-bit LFSR (indicated as C7 in the Control Unit circuit board) which generates the PN (pseudo noise) sequence.
 
Fig. 2 - the initial "sync template" sequence (demod speed: 220Bd)
 
The sync template is then followed by the  so-called "Additional Key" (AK): a time and key-dependent 64-bit block which is tree times repeated and sent in clear-text ASCII 8N2 at the speed of 110 Baud (Figure 3, in opposite polarity). The correct additional key information is obtained by majority decision from the three additional key blocks, which are identical under good transmission conditions, and mixed with the basic key to initialize the cipher generator at the receive TC-535 (thus the AK field may be termed as the Initialization Vector for TC-535).
 
Fig. 3 - the tree 64-bit Additional Key blocks (demod speed: 110Bd)

The sync phase (PN + AKs) is then followed by a 22-bit long alternating sequence of "0"s and "1"s  which separates AK blocks from encrypted data and allows the speed change to 220Bd (Figure 4).
 
Fig. 4 - 22-bit "01" sequence, also visible in Fig. 2, unless some bit in error (demod speed: 220Bd)

An optionally switchable FEC protection is built into the TC-535. If FEC is enabled, additional check bits are added to the data, which increase the data volume by a factor of 1.4 to 2.0 depending on the user code (Baudot/ASCII). In case of ASCII, the inserted check bits reduce the useful bit rate to half and consequently bit rate shall be increased by a factor of 2, thus the 220 Baud since the ASCII operational speed is 110 Baud. This clarifies the initial 110 Baud speed used to send the AK blocks (sent as async, clear-text, no FEC)! Note that the encrypted data are only transmitted in synchronous mode and returned asynchronously to the data sink.
The doubled data volume means that FEC encoder function is accomplished by a rate 1/2 convolutional coder (as indeed confirmed in [2], "Encryption method: Bitstream encryption"). Thus, the 220 Baud speed is a sign that FEC is activated and user data are ASCII coded. 
 
About the canche to trace a check matrix/polynomial in the streams, it should be noted that documentation says "The check bits are obtained from useful bits that have already been sent and added to the data to be sent before encryption", thus FEC encoding happens before the encryption process (!) and unfortunately there will be no interesting signs to look for in the streams. 
However, it can be noted that sometimes a single transmission carries more than one AK blocks (Figure 5), so we think that a single transmission may carry multiple messages/files, each preceded - most likely - by an appropriate an PN sequence.

Fig. 5 (demod speed: 220Bd)

TMS-430 (TelematikSet 430) consists of an NEMP-protected (protection against Nuclear ElectroMagnetic Pulses) device set in a large fiberglass box, consisting of: a notebook computer Toshiba 110CS, Pentium 100 MHz, VGA screen 11.3 inches, an Epson LX 300 matrix printer, two boot disks with DOS - based software.The (in the meantime no longer completely up-to-date) notebook is equipped with a hard drive, but is intended to be started from a boot floppy disk, if necessary any other commercially available IBM-compatible computer can be used. The messages to be transmitted can be recorded directly on the system, but usually a diskette is used to transfer the text message from the command post to the transmission office.
TC-535 (TeleCrypto 535) is more than "just" an encryption device since it also automatically controls the change of direction of the radio stations involved in the link. The most important features are the time and key-dependent initialization sequence, random filler text when in idle and the non-disruptive change of direction. The device is controlled via the TmS-430 keyboard.
As said, the utilized HF transceiver should be the SE-430. The complete communications system consists of a control unit (BE-430), usually connected to a encrypter, and a radioteletype machine. The signal is transferred over field telephone lines to the transmitter site, which can be installed at quite a long distance. The transmitter site equipment consists of the transmitter SE-430, it's power supply SG-430 and the automated antenna tuner AG-510/430.

Fig. 6 - TMS-430 (on the left) and TC-535 (source: Historisches Armeematerial Führungsunterstützung HAMFU)

https://yadi.sk/d/8xDdmoSlMhEJig
 

28 August 2020

CIS Navy VLF 50Bd/75 FSK (T600 75Hz)

50Bd/75 FSK is the T600 waveform variant utilized by Russian Navy on 18.1 kHz, commonly for submarine communications.

Fig. 1 - 50Bd/75 waveform
As seen in CIS 36-50, frames are constructed from data blocks consisting of 7-bit words: a packet of payload data of basically arbitrary length is surrounded by a start and an end sequence (EOM). Sometimes blocks of data already transmitted are observed to be repeated, verifying the contents by the recipient can be performed easily this way. Idle sequences of reversals, i.e. strictly alternating sequences of "0"s and "1"s, of 36 Bd and 50 Bd are used to introduce and to terminate a transmission or also (50 Bd only) to separate data blocks.
A data block itself consists of three sections: start sequence, (encrypted) payload data, end of message (EOM) sequence; all payload data has a fixed ratio of '1's vs. '0's of 4 to 3 or vice versa, depending on polarity of reception (Figure 2). 

Fig. 2 - 4/3 ratio test on a five-message transmission (s1 and s2 data blocks are the same)
After a single "1" bit (following the last "01" reversal pair), the 28-bit (four-words) start sequence 1010111 1101011 0100000 1010000 is sent: the 4/3 ratio is not followed here to make the start sequence distinguishable from the actual data. Payload comes next; its first part are two equal words 0101101 0101101 followed by a repeated ten-word (7 bits each) group: likely the Message Indicator or the session key. All subsequent data (arbitrary length) do not obey a special regularity anymore. The end sequence shows five equal 7-bit words (5 x 0001000), again disregarding the 4/3 ratio of the data section (Figure 3).
Fig. 3 - structure of a data block

Multiple Russian military naval communication stations share this frequency (18.10 KHz) and the call sign "RDL".  The 24h transmission schedule has frequent flash-override messages in A1A Morse, FSK-Morse and T600 75 Hz, as shown in the lower image of Figure 1.

https://yadi.sk/d/0M7f_H_WOD9LTA (T600-75 bitstream)

22 August 2020

Swedish Navy submarine MSK multi-channel broadcast


(For background it might be helpful to read the relevant entries here)

Swedish Royal Navy (Swedish: Svenska marinen [1]) uses a broadcast function of STANAG-5030 (1) for communication with its subs in the Baltic Sea, the return channel is believed to be low-end HF. These LF broadcasts use the 200Bd/100 MSK waveform and can be heard on 40.4, 42.5, and 44.2 KHz (CF) by using  KiwiSDR receivers located in the island of Gotland which have a good SNR. [2].

All the three signals have the classic set of parameters for (G)MSK: a spectrum equal to 1.5*Br (300Hz), shift equal to Br/2 (100Hz), a characteristic bell-shaped appearance (Figure 1), and others such as 4-point constellation, transitions and real trajectories (Figure 2). Please note that the carrier in the fourth degree is very weakly expressed, sometimes it is practically invisible at all.

Fig. 1
Fig. 2
Using 200Bd MSK (a form of QPSK) it is possible to transmit two 100 Baud channels X and Y, each on a pair of phase, and each channel can consists of 2x50 Baud multiplexed channels. Thus, MSK can provide a TDM multi-channel broadcast of  up to 4x50 Baud X1 X2 Y1 Y2 channels within the 200Hz assigned band (MSK4).  Some aspects about the similarities bewteen QPSK and MSK are covered in radioscanner forum [3].

In conditions where no messages are available for transmission, the four channels are arranegd with two "empty channel filler" (ECF) patterns, probably generated automatically at the transmitter equipment:
- two channels share the same 15-bit pattern;
- a third channel uses a different 5-bit pattern;
- the fourth channel uses the same 5-bit pattern where one column is repalced by the bits of the pseuso-random sequence generated by the polynomial x^31+x^3+1.
An example of this "idle" mode is shown in Figure 4: here the m-sequence is sent in the Y2 channel (notice the same pattern sent in X1 X2 channels ).

Fig. 3
A more generalized scheme highlighting the position of the m-sequence channel in four different recordings is shown in Figure 4.

Fig. 4
 In case of messages, the four channels use a 5-bit format with different framings:  
- two channels share the same 5-bit framing, i.e 1-bit marker (pos/neg according the polarity) + 4-bit data:
- a third channel uses an unid (to me) framing;
- the fourth channel uses the same 5-bit framing of the first two channels but the marker column is replaced by the bits of the pseuso-random sequence generated by the polynomial x^31+x^3+1.
Figures 5a,5b show such arrangement.

Fig. 5a
Fig. 5b
Due to their strategic and tactical importance, subcomms require secure cryptographic protocols and this could explain the presence of the x^31+x^3+1 pseudo-ramdom sequence which is used to sync the receive KW-46/KIV-7 ciphers (other than to permit channel identification), although an encrypted 4-bit stream is rather unusual as well as the use of the 1+4 bits frames. 
In this regard, one might even think that the actual secured messages channel is Y before the TDM split (Figure 6), while the other channels X1 X2 transport not critical 4-bit coded data (WX forecast, sea conditions, ...). This way, messages could use 10-bit START-STOP code which is then encrypted using the KW-46/KIV-7 equipment. Encryption results in bits 2 to 10 being encrypted and bit 1 (START) being replaced with unencrypted bit defined by the polynomial x^31+x^3+1, or in reverse order - bits 1 to 9 encrypted and bit 10 (STOP) replaced (2). A second hypothesis - perhaps the most likely - is that each channel is encrypted with a specific cipher ...but these are just my speculations.

Fig. 6 (m-sequence columns are highlighted)

The results of TD0A geolocation indicate three probable transmitter sites that match fairly exactly with those indicated in a map presented by FMV (the Swedish Defence Materiel Administration) [4] at the March 2020 HFIA HF Industry Association [5] Meeting in San Diego, CA (Figure 7):
- 40.4 KHz: SAS/SRC Varberg
- 42.5 KHz: SAS2 Gudinge
- 44.2 KHz: SHR Ruda

Fig. 7

It must be taken into account that I can't record the (KiwiSDR) LF spectrum 24/7 so the results indicated above may be incomplete: further recordings are needed and possibly an update post will be published later. Hints and comments are welcome.


(1) STANAG-5030 is a restricted document so no information is publicy available. Moreover, the new STANAG-4724 "VLF/LF MSK Multi Channel Broadcast" is currently being ratified by NATO member states as next evolution:

(2) max success for x^31+x^3+1 in Y stream was found for a length frame of 10 bit; that same frame does not have parity bits (x^31+x^3+1 column excluded from the checksum)


4 August 2020

(yet another) 100Bd/500 FSK-2


4 August 2020 update
some frequency, same timing, and same 511-bit sequence but the speed has switched to 50Bd (shift remains unchanged, 500Hz):


It's to notice that the 511-bit sequence is obtained using the seed  s=[0 0 0 0 0 0 0 0 1]  and transmitting the output in opposite polarity (i.e., inverting the polarity of the demodulated sequence we get the exact sequence generated with seed s=[0 0 0 0 0 0 0 0 1]):

up: LFSR sequence when seed = [0 0 0 0 0 0 0 0 1], down: received sequence after reversing the polarity

2 August 2020
Just to log interesting 100Bd/500 FSK-2 transmissions found on 9130 KHz (CF). Data sent consist of a repeated 511-bit pseudo-random sequence which is generated by the polynomial x^9+x^5+1 (Fig. 1); likely that sequence is used when no data to transmit is available or to mantain sync between transmitting and receive modem (see also ITU Recommendation O.153 [1]). Since the 100Bd/500Hz waveform is used in several systems, it's difficult to state the source; anyway, it's to notice that x^9+x^5+1 sequences (PRBS9) are also used in CIS-12 and more generally in T-230 family devices.

Fig. 1 - the 511-bit pseudo-random sequence

Looking at the two FSK tones, it seems that they preserve their phase after each switch-over (Fig. 2). By the way: F1 = 753.87 Hz (1:0.001326479), F2 = 1253.68 Hz (2:0.001595299), dF = 499.81 Hz.

Fig. 2

I followed the transmissions for some days, they usually take place on weekdays at 0943 and stop at 1100 (UTC times). I ran several TDoA attempts and results point to the Moscow area, unfortunately they do not exactly agree.

Fig. 3 - start stop period

Fig. 4 - some of the TDoA results


27 July 2020

CIS-11 (TORG 10/11)

CIS-11 (also designated as TORG 10/11) is a synchronous, duplex ARQ system requiring separate forward and return links. It's used mainly for aeronautical weather reports in CIS, thus transmissions normally take place in M2 alphabet (Cyrillic third-shift ITA-2). Modulation used is FSK2, usually 100Bd and 500Hz shift with 11-bit period (figure 1).

Fig. 11
Its characteristic 11-bit format consists of the 5 bits of the ITA-2 alphabet d4-d0 (but in reversed bit order: d0-d4), 2 system state bits s0 and s1 and 4 parity bits p0-p4: the checksum is calculated by modulo-2 addition from all 7 other bits (d4-d0 + s0-s1) as: 

p0 = d1 + d3 + d4 + s0
p1 = d0 + d2 + d4
p2 = d0 + d1 + d3 + s1
p3 = d0 + d2 + d3 + s0 + s1

Fig. 2
I wrote a simple Octave script (CIS11_detect.m) just to check CIS-11 streams and extract the 5-bit data in case of  successful result:

## usage: CIS11_detect(fn,e)
## input:  fn ... filename containing a string of 0's and 1's (no space between)
##         e  ... 0 doesn't exctract data
##            ... 1 extracts M2 data
## output: m  ... CIS-11 parity bits success [0..1]
##         a  ... aligned bit frames: parity bits in a(8:14), in case m > 0.9
##         fn_M2-data.txt
##                ASCII file with the exctracted data, in case m > 0.9 and e = 1

CIS11_detect is downloadable from:
(you will need the GNU Octave package [1] to run the script).

I checked two transmissions and results are shown in Figs. 3,4; note the values of the system state bits (the two solid columns) in the two streams.
Fig. 3
Fig. 4
The system state bits signal the link state and traffic information, below a possible relationship just based on the (few) analyzed recordings:
00   - idle or Request
01   - ?
10   - Cyrillic
11   - Latin
transition to Cyrillic traffic is signaled by 00000 10
transition to Latin traffic is signalled by 11111 11

CIS-11 uses also two "idle signals", according to ITU-R F.342-2 [2]): idle signal α "01101 00 1100" is used when no data to transmit is available and mantains sync between transmitting and receive modems; idle signal β "10101 00 0001" is the ARQ request character. It's to note that:
- both the idle signals have the system state bits set to 00
- if shifted(!) the idle signal β is CIS-11 compliant (look at start bit offset in Fig.5)
- idle signal α is a LFSR x^3+x^2+1 sequence, the 7-bit sequence is used in d0-d4,s0-s1 bits
- idle signal β can be scrambled using the LFSR x^5+x^4+1

Fig. 5

CIS-81-81 (81-81, Moroz) T-206

update
A friend of mine sent me an interesting comment about the 6 and 12 bit formats used in CIS-81-81 mode, likely they refer to a former version of 81-81 and clear-text transmissions:

6-bit format (40.5 Bd): idle and traffic

12-bit format (81 Bd), two cahannels "a" and "b", bit-interleaved:


a) Channel a and b idle
b) Channel a traffic
c) Channel b traffic
d) Channel a and b traffic


(bits 2 and 5 are sent in inverted polarity).


July, 21 
Since in the last few weeks I have encountered mostly FSK2 signals (mostly from the East), I decided to take a slightly deeper look at "old" FSK2 modes such as CIS-81-81 and CIS-11 (the latter in a next post).
CIS-81-81, also designated as 81-81 (1) , T206-M 3M1 device, is the dual channel version of CIS-40.5 mode, hence the designation 81-81; "Moroz" ("FROST" in English) is just an old nickname for the mode [1]. Most likely, when operating in two channels the data are transmitted using time division multiplexing. Both 40.5 and 81 are quite "old" systems, most likely also in use by some ex USSR republic. Speculation is that this older 81-81 system, as defined above, is no longer in use and that the newer 81-81 system is most likely to be derived from CIS-14 or CIS-27 system (81-29 designation?) [2]. Some old reports from WUN logs indicate different users of these systems [2].

Shift           Common User
-------------------------------
125             Navy   
500             Railway Authority
200,250,500,    Military
1000,1500


So far, I have at my disposal CIS-81 samples in two different shift patterns:

81Bd 250
Fig. 1
It's the 81-81 most interesting waveform since its demodulated stream exhibits a 24-bit pattern due to the  length of the idle signal which consists of 12 mark and 12 space bits (notice that CIS-40.5 250 uses 12-bit idle signal consisting of 6 mark and 6 space bits). The sequence generated by x^11+x^9+1 (PRBS11)  is used to scramble to the following data block or symply as "test" message; then the idle signal is repeated in opposite polarity (Fig. 3). Traffic in the channels is encrypted. It's worth noting that the polynomial and the idle signal "format" are the same in the 250Hz shift patterns of CIS 40.5 and 81 Baud.

Fig. 2 - CIS-81-81 250 

Fig.3


81Bd 500
Although the lack of the idle signals (at least in this recording), the demodulated stream is very interesting since it too can be descrambled using  the polynomial x^11+x^9+1 (Fig. 5).

Fig.4
Fig.5
 
T-206 MT "WESNA" (T-206 MT, T-206 2MT, T-206 3M und T-206 3M1)
T-206 is a Soviet teletype and data encryption family devices (not a modem!) used in stationary and mobile operation [3].

Fig. 5 - T206 MT [3]

(1)
The system has it roots in the synchronous, manual Baudot printing telegraph system whcih was used extensively already in Imperial Russia. The telegraph network of Imperial Russia was of course inherited by the Soviet Union, where the political leadership very soon realized that good telecommunications were at the roots of its modernization project. During and after WWII teleprinting was extended to radio links using either A1 or F1 modulation. It was therefore natural to adapt the old Baudot system to radio transmission and reception. As the system was synchronous its frame format needed a means to tell whether the link was active or idle, consequently a status bit was added in front of the five data bits yielding a 6-bit frame. For 2-channel systems this was naturally expanded to 2 x (1+5) = 12 bits. The system would then be transmitted as frame or bit interleaved. These systems used the first version of the International Telegraph Alphabet (ITA 1).

https://yadi.sk/d/WQikSYo77Z6oBA (250Hz shift, #1)
https://yadi.sk/d/bd81CpHyBFDuCQ (250Hz shift, #2) 
https://yadi.sk/d/-Q-4JagM1eeBHw (500Hz shift)                     

17 July 2020

CIS-14 FSK 100Bd/2000 (CIS 3x100)

Interesting 100Bd/2000 FSK signal spotted on 16059.5 KHz (CF), most likely a Russian Governative transmission. This signal is not a separate one, actually it must be considered as part of the CIS 3x100 "system" visible on the left in figure 1. Indeed, the main station operates a VFT 3x100bd/1440 signal and works simultaneously three outstations which in turn run the FSK 100Bd/2000 waveform (outstations are usually not far apart in frequency).

Fig. 1
As well as the mainstation (VFT 3x100Bd/1140), outstations too use CIS-14/T-207 (as from the analysis of the demodulated stream in figure 2); all use the same checksum mode [0312].
Fig. 2
A clearer illustration of this "system" is visible in the spectrum of figure 3, the IQ recording of which was provided by my friend KarapuZ [1] who discussed the signal here.

Fig. 3

14 July 2020

demodulating sync F7B mode transmissions using F7B.exe software

F7B signal, apparently a "classic" MFSK-4
My friend cryptomaster coded a program (F7B.exe) for demodulating synchronous F7B, it can be freely used and distributed for the analysis of such signals. Unfortunately, SA program parses these transmissions as classic MFSK-4 but that is not what actually is on-air: indeed,  F7B transmission mode deals with signals consisting of two independent but synchronous channels CH1 CH2 each carrying teletype signals (FSK2 on 2 independent channels).

F7B.exe can be downloaded from here:
Warning: F7B.exe is coded to run under win/32-bit systems so you may encounter a comdlg32.ocx error (component not correctly registered) when try to run it under x64 systems, here is how to resolve comdlg32.ocx missing error:
https://www.swisssalary.ch/.../register-comdlg32.ocx-on-x64-win7

F7B.exe needs as input file the  raw MFSK-4 stream produced by the demodulator of SA and output two ASCII-Bit files CH1.txt and CH2.txt in the same directory of the input file:


Moreover, the Octave script T207_detect.m  has been used for the check of T207/CIS-14 mode [1]: it can be freely downloaded from here (you will need GNU Octave package [2] to run the script):
https://github.com/hcab14/.../T207_detect.m
the Octave script T207_detect_e.m also extracts the two world and bit interleaved channels:
https://yadi.sk/d/zsCD73C9DZpHPQ

I tested the demodulator on the two  F7B modes 100Bd/1000 and 96Bd/500, both actively used by Ukrainian Nets; by the way, two preliminary observations:

1) usually, the two F7B channels CH1 CH2 are T-207 secured according to the CIS-14 mode [1]. Since CIS-14 consists of two independent 5-bit MTK-2 channels (transmitted in 14-bit frames), it turns out that those F7B transmissions may carry up to four independent 5-bit channels (CH1a, CH1b, CH2a, CH2b);

2) both those F7B waveforms have their FSK2 counterparts.

I also tested F7B.exe on the Rockwell TE-204, a "special" time-frequency diversity FSK4 mode most commonly used by Allied Air Forces as an air-to-ground messaging system as well as in ground and naval applications.

100Bd/1000 F7B

Fig. 1 - 100Bd/1000 F7B
100Bd/1000 F7B transmissions occupies about 3000Hz bandwidth with the four tones at -1500, -500, +500, +1500 Hz respect to the center frequency. As said above, 100Bd/1000 F7B transmissions may carry up to four independent 5-bit channels. In this regard, it's worth noting in figure 2 that - at least in this sample - the two F7B channels adopt different CIS-14 checksums: mode 20 (0312) in channel CH1 and mode 3 (3120) in channel CH2: who knows, maybe the two F7B channels carry the same data but with different checksums just to increase the redundancy of the system. Note that CIS-14 100Bd/1000  (the FSK2 counterpart) uses the checksum mode 20.


Fig. 2 - two 100Bd/1000 F7B channels, each transporting two CIS-14 channels (CH1a, CH1b, CH2a, CH2b)

96Bd/500 F7B
Fig. 3 - 96Bd/500 F7B
96Bd/500 F7B transmissions occupies about 1500Hz bandwidth with the four tones at -750, -250, +250, + 750 Hz respect to the center frequency. The same earlier conclusion applies: that is since CIS-14 consists of two independent channels,  96Bd/500 F7B transmissions too may carry up to four independent 5-bit channels.
I don't know if it's a mere coincidence, anyway it's interesting to note in figures 4,5 that only one channel transports data, as well as the CIS-14 96Bd/500 (the FSK2 counterpart) does: i.e., either 96Bd/500 F7B either 96Bd/500 FSK2 use only one of their two "available" channels.  Both the waveforms use the CIS-14 checksum mode 20.

Fig. 4 - two 96Bd/500 F7B channels, only one of the two available CIS-14 channels is used

Fig. 5 - CIS-14 96Bd/500 FSK2 channels, only one of the two available 5-bit channels is used
In this transmission the two channels use different EOT signaling sequences (figure 6)

Fig. 5

Rockwell TE-204 FSK4
Although TE-204 does not definitely use the F7B mode, I decided to check it since regards two FSK2 channels. Indeed, TE-204 transmits the "mark" on 935 Hz for 6.67 msec period followed by a replicated 6.67 msec "mark" at 1815 Hz. Similarly, the "space" is transmitted at 1375 Hz for 6.67 msec followed by a replicated 6.67 msec "space" at 2255 Hz (figure 6). This "mode" provides an in-band frequency  and time diversity function  (thus the speed is the half of the measured one). As for above, from the perspective of the  data-transfer, the modem works as a 75Bd/880Hz FSK2 modem.

Fig. 6
Well, decoding separately the two FSK2 channels (935-1375, 1815-2255) we get obviously two time-shifted similar streams (figure 7)

Fig. 7 - the two TE-204 demodulated FSK2 streams
Demodulating it as if it were an F7B signal we get "01" sequences in channel CH1 and  (expected) duplicated data in channel CH2 (figure 8)

Fig. 8

https://yadi.sk/d/f0U80pRg3F58iA  (F7B signals)

[1] https://i56578-swl.blogspot.com/.../redefining-t-207-checksums.html
[2] https://www.gnu.org/software/octave/